Pre-cats: The Official MR2-ROC Information Thread

[sailingsmith]

Hi there it took me two hours from start to finish, but everything came off with no problems. If you look at the thread , pre cat removal how I did it, page 15 there is a link to spyderweb where you can see pictures on how to do.
Hope this helps.

That's good to know Lurch, so if I allow half a day then that will be fine. I just didn't want to end up with the car out of action for ages after I just pick it up.

[RubixRonnie]

Precats out or just replace the whole manifold?thoughts?

[HughG]

Hello, first post here, which is a very helpful forum. I picked up a 54plate with 47k yesterday. It has a TTE exhaust which was mentioned earlier in the thread as having metal precats instead of ceramics. Please can someone confirm this.

Also is it possible that the TTE system could have been fitted later cat back? In which case is there any way to check whether I have the TTE manifold without removing it to check what the honeycomb is made from.

Thanks
Hugh

[Wabbitkilla]

TTE exhaust is only a cat back system so you still have your original catalyst and manifold (with precats).

You may have confused this with the TTE turbo which does have metal precats.

[Suzz381]

Ummmm, I've got a 56 reg mr2. It's on 32k at the mo.
Read somewhere that the pre cat prob had been fixed by 2006 models? Does anyone know if this is the case or should I be getting the pre cats checked??

[Roadster]

Is there an easy way to see if a previous owner has removed the pre-cats? i've got a 2000 model with 44k miles, spent it's entire life on an island  with a maximum speed limit of 35mph, I've read the ways to check the state of the pre-cats on the first post but is there anything noticeable you can check to see if someone has already removed them?

[Joesson]

I am sure the only way to tell if they have been removed is as stated in the first post: Remove the two O2 sensors.
As stated this is best done with a made for purpose socket spanner.
If you do not have one there may be  ROC member near to you with one or order one from the www.
Either way while you are waiting for the spanner (if you are not using the car) soak the sensor /manifold joint with PlusGas or similar penetrating fluid.
If your 2 has lived its life at such sub sonic speed you will likely need to check/clean or replace the spark plugs and clean the MAF.
Important, enjoy!

[GT4thomas]

Mine look like this. Big power loss, struggles to rev

[andyroo104]

There is not a lot left,hence your power loss. s:-( :-( s:-(

[Roadster]

I am sure the only way to tell if they have been removed is as stated in the first post: Remove the two O2 sensors.
As stated this is best done with a made for purpose socket spanner.
If you do not have one there may be  ROC member near to you with one or order one from the www.
Either way while you are waiting for the spanner (if you are not using the car) soak the sensor /manifold joint with PlusGas or similar penetrating fluid.
If your 2 has lived its life at such sub sonic speed you will likely need to check/clean or replace the spark plugs and clean the MAF.
Important, enjoy!

Thanks  s;) s;)

[shnazzle]

I've recently done a pre-cat removal and have a few thoughts/observations that may be of interest. First I will summarize my recommendations, prioritised:
1) Get an aftermarket manifold (someone sent me a link for a 90 quid one which is good)
2) Wrap the manifold in heat wrap
3) consider exhaust situation with pre-cat removal

Now I shall explain:

I gutted my manifold and cleaned it out. Fairly straight-forward procedure as described on the first post. I had no issues at all with bolts, but as I spent almost 70 quid on new ones and gaskets...figured I might as well replace them. I cleaned out the manifold after gutting it with a variety of products to make sure it was nice and clean.
I also added a TTE Exhaust at the same time...this may or may not contribute to my observations.

I noticed one main thing on a good run out; there is a clear difference in power delivery. Both good and bad.
The very first time I took it out I noticed an increase in low-down torque. This makes sense. The exhaust is more free-flowing without pre-cats and the TTE exhaust which is less restrictive. I was a happy camper.
Then I noticed, it has lost some "oomph" in high load.

Theory behind it (in my opinion): Initial torque is increase as the exhaust system is less restricted and air flow is not at max. There isn't much pressure behind the exhaust, so it flows happily straight through the manifold and out the exhaust. Happy days!

Now in high load there's something new; there's now two nice big empty chambers where the pre-cats used to be. You mash the loud pedal at 50-ish mph and exhaust rushes into the manifold and into the big empty chambers, wanting to continue rushing out. Instead, it finds the narrowed opening from the pre-cats to the main cat. Now there's a queue of exhaust gas building in the chambers as all the little exhaust molecules line up single-file to get into the cat converter in an orderly British queuing fashion. The queue builds up and now there's a blockage. More exhaust comes flying in from the engine and is now hits the back of the queue. Back-pressure! Now opening up the exhaust too much is also not good. We know we need to keep the velocity of exhaust gasses up to keep a good flow. Air flows faster through a straw than it does through a sewage pipe given the same input. But do we really want to have exhaust gas almost making its way back to the exhaust valves?  ...I don't.
Engine is now no longer running efficiently and loses some torque/pull.

So yes, removing pre-cats is a good thing. Especially on a 2004-ish or earlier car of course, as said before. Peace of mind etc etc bla bla. But it would be great if someone could measure the impact of this on a dyno and maybe check the exhaust valves pre and post cat removal, after a few thousand miles to prove/disprove my theory.

In the meantime, if I were to redo this, I'd get an aftermarket manifold and wrap it. I took my heatshields off, and ran it like that for a bit and the heat in the engine bay was just ridiculous. Who knew exhaust manifolds got so hot?!?!  hahaha...I kid...
I bought 10 quid of exahust heat wrap from "the bay" and spent 30 minutes wrapping it. Had a hard 45 minute run up Hartside pass and afterwards opened up my engine bay and was actually able to  touch my manifold (don't ask why I tried). So it makes a huge difference. Much better than heat shields.

My 2-pence...done.

[James and his MR2]

I once had a pop on the standard exhaust...  s;) s;)  (gutted precats)

[shnazzle]

I once had a pop on the standard exhaust...  s;) s;)  (gutted precats)

I'm popping all over the place now. It's not loud at all. But I can just hear it when I let off

[jinxedkitten]

I'm popping all over the place now. It's not loud at all. But I can just hear it when I let off

Don't eat so many beans then. Must confess, love a good exhaust pop/bang/grumble  s:) s:)

[Roadster]

Surely this 'popping' can't be good for the car either? if most cars don't have pre-cats how does the gas travel through it without building up and popping?

[shnazzle]

Surely this 'popping' can't be good for the car either? if most cars don't have pre-cats how does the gas travel through it without building up and popping?

If you read my lengthy post above.... I think removing pre-cats actually reduces performance overall. Unproven. But just what I've noticed

[Roadster]

Surely this 'popping' can't be good for the car either? if most cars don't have pre-cats how does the gas travel through it without building up and popping?

If you read my lengthy post above.... I think removing pre-cats actually reduces performance overall. Unproven. But just what I've noticed

I read it, I know it's unproven but your not the only person to mention a popping sound when they are removed, is it a minority which get the popping sound do you think?

[shnazzle]

I read it, I know it's unproven but you're not the only person to mention a popping sound when they are removed, is it a minority which get the popping sound do you think?

It's not particularly audible on mine,  and that's with the TTE exhaust. You can hear it pop internally a bit.
So most people won't realise it I reckon. Not a problem with free flowing after market manifolds.

Mind,  I don't think the popping is a bad thing. It's not banging. Just sounds like healthy,  normal popping made more audible by the open pre-cats chambers

[Roadster]

I was able to take the right o2 sensor out to take a look at the precats from the top but i'm struggling to take the left one out, I've used loads of PlusGas but even my brother (who is fairly strong) isn't able to get the bolt off the left one, i'm turning it anti-clockwise just like the one on the right but this one won't budge, the one on the right was replaced by a previous owner not too long ago so wasn't too hard.

Is there anything else i can do to remove this o2 sensor without breaking it?

[Joesson]

Has the Plus gas been allowed to work for some hours?
Are you using a slotted socket?
If so this could be limiting the torque applied to the sensor as the slot in theory will allow the socket to gape.
As you need to replace it anyway I would cut off  the cable and then try with a six sided regular socket with an extension and and a wrecking bar or a piece of heavy gauge tubing to increase the leverage.
Keep the socket pushed well down onto the sensor.
If still no movement heat will be your friend.
Some have had success with running the engine to heat the manifold.
Others have tried applying heat to the manifold area around the sensor with a blowtorch.
Warning, as recently noted, Plus Gas is flammable.
A case for the 3 P's again I think.

[loadswine]

With one sensor removed, it should be possible to remove the heatshield. With that out of the way, you should be able to get a 22mm ring spanner on the stubborn sensor. Might be worth trying a bit of heat as well. Threads have been known to strip with really stubborn sensors. There is no predicting that, unfortunately.

[Roadster]

Has the Plus gas been allowed to work for some hours?
Are you using a slotted socket?
If so this could be limiting the torque applied to the sensor as the slot in theory will allow the socket to gape.
As you need to replace it anyway I would cut off  the cable and then try with a six sided regular socket with an extension and and a wrecking bar or a piece of heavy gauge tubing to increase the leverage.
Keep the socket pushed well down onto the sensor.
If still no movement heat will be your friend.
Some have had success with running the engine to heat the manifold.
Others have tried applying heat to the manifold area around the sensor with a blowtorch.
Warning, as recently noted, Plus Gas is flammable.
A case for the 3 P's again I think.

I'm using a 02 sensor socket 22mm on a ratchet, I have to replace the cable? do you mean if i force the sensor out?, ill try an extention without cutting the cable if i can, from what i can tell from the right precat they are starting to go, but if i take them out ill need to get this left sensor out anyways, lol after yesterday i'm quite aware of the flammability of the PlusGas   s:lol: :lol: s:lol:

With one sensor removed, it should be possible to remove the heatshield. With that out of the way, you should be able to get a 22mm ring spanner on the stubborn sensor. Might be worth trying a bit of heat as well. Threads have been known to strip with really stubborn sensors. There is no predicting that, unfortunately.

The bolts at the top of the heat shield have pretty much disintegrated, which was my next question when i plan to remove these precats in a couple weeks, it's a 2000 model and has done 44k miles and spent it's life in Guernsey (A tiny island 35 miles around the entire coast) with a maximum speed limit of 35MPH ...some of the precat is looks a bit bad

[Joesson]

Sorry, I understood the sensor was not working. It certainly wouldn't if you cut the cable.
As loadswine pointed out it is much easier to access the sensor with the heatshield removed. That is if the heatshield wants to come off!

[loadswine]

For the dodgy heatshield bolts, Irwins may work, or it will be a matter of drilling the bolt heads off and seeing if you can get the remainder out with stud extractors.

[Roadster]

For the dodgy heatshield bolts, Irwins may work, or it will be a matter of drilling the bolt heads off and seeing if you can get the remainder out with stud extractors.

You mean these?  m http://www.homebase.co.uk/en/homebaseuk ... :1o5|bku:1 m  

my right precats  m http://postimg.org/gallery/1qbjtoca/41e137a9/ m

Would you say they are.  not bad or getting there or urgent?